// SPDX-License-Identifier: GPL-2.0-only /* * fs/kernfs/mount.c - kernfs mount implementation * * Copyright (c) 2001-3 Patrick Mochel * Copyright (c) 2007 SUSE Linux Products GmbH * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org> */ #include <linux/fs.h> #include <linux/mount.h> #include <linux/init.h> #include <linux/magic.h> #include <linux/slab.h> #include <linux/pagemap.h> #include <linux/namei.h> #include <linux/seq_file.h> #include <linux/exportfs.h> #include "kernfs-internal.h" struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache; struct kernfs_global_locks *kernfs_locks; static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry) { struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry)); struct kernfs_syscall_ops *scops = root->syscall_ops; if (scops && scops->show_options) return scops->show_options(sf, root); return 0; } static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry) { struct kernfs_node *node = kernfs_dentry_node(dentry); struct kernfs_root *root = kernfs_root(node); struct kernfs_syscall_ops *scops = root->syscall_ops; if (scops && scops->show_path) return scops->show_path(sf, node, root); seq_dentry(sf, dentry, " \t\n\\"); return 0; } const struct super_operations kernfs_sops = { .statfs = simple_statfs, .drop_inode = generic_delete_inode, .evict_inode = kernfs_evict_inode, .show_options = kernfs_sop_show_options, .show_path = kernfs_sop_show_path, }; static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len, struct inode *parent) { struct kernfs_node *kn = inode->i_private; if (*max_len < 2) { *max_len = 2; return FILEID_INVALID; } *max_len = 2; *(u64 *)fh = kn->id; return FILEID_KERNFS; } static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid, int fh_len, int fh_type, bool get_parent) { struct kernfs_super_info *info = kernfs_info(sb); struct kernfs_node *kn; struct inode *inode; u64 id; if (fh_len < 2) return NULL; switch (fh_type) { case FILEID_KERNFS: id = *(u64 *)fid; break; case FILEID_INO32_GEN: case FILEID_INO32_GEN_PARENT: /* * blk_log_action() exposes "LOW32,HIGH32" pair without * type and userland can call us with generic fid * constructed from them. Combine it back to ID. See * blk_log_action(). */ id = ((u64)fid->i32.gen << 32) | fid->i32.ino; break; default: return NULL; } kn = kernfs_find_and_get_node_by_id(info->root, id); if (!kn) return ERR_PTR(-ESTALE); if (get_parent) { struct kernfs_node *parent; parent = kernfs_get_parent(kn); kernfs_put(kn); kn = parent; if (!kn) return ERR_PTR(-ESTALE); } inode = kernfs_get_inode(sb, kn); kernfs_put(kn); if (!inode) return ERR_PTR(-ESTALE); return d_obtain_alias(inode); } static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid, int fh_len, int fh_type) { return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false); } static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid, int fh_len, int fh_type) { return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true); } static struct dentry *kernfs_get_parent_dentry(struct dentry *child) { struct kernfs_node *kn = kernfs_dentry_node(child); return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent)); } static const struct export_operations kernfs_export_ops = { .encode_fh = kernfs_encode_fh, .fh_to_dentry = kernfs_fh_to_dentry, .fh_to_parent = kernfs_fh_to_parent, .get_parent = kernfs_get_parent_dentry, }; /** * kernfs_root_from_sb - determine kernfs_root associated with a super_block * @sb: the super_block in question * * Return the kernfs_root associated with @sb. If @sb is not a kernfs one, * %NULL is returned. */ struct kernfs_root *kernfs_root_from_sb(struct super_block *sb) { if (sb->s_op == &kernfs_sops) return kernfs_info(sb)->root; return NULL; } /* * find the next ancestor in the path down to @child, where @parent was the * ancestor whose descendant we want to find. * * Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root * node. If @parent is b, then we return the node for c. * Passing in d as @parent is not ok. */ static struct kernfs_node *find_next_ancestor(struct kernfs_node *child, struct kernfs_node *parent) { if (child == parent) { pr_crit_once("BUG in find_next_ancestor: called with parent == child"); return NULL; } while (child->parent != parent) { if (!child->parent) return NULL; child = child->parent; } return child; } /** * kernfs_node_dentry - get a dentry for the given kernfs_node * @kn: kernfs_node for which a dentry is needed * @sb: the kernfs super_block */ struct dentry *kernfs_node_dentry(struct kernfs_node *kn, struct super_block *sb) { struct dentry *dentry; struct kernfs_node *knparent = NULL; BUG_ON(sb->s_op != &kernfs_sops); dentry = dget(sb->s_root); /* Check if this is the root kernfs_node */ if (!kn->parent) return dentry; knparent = find_next_ancestor(kn, NULL); if (WARN_ON(!knparent)) { dput(dentry); return ERR_PTR(-EINVAL); } do { struct dentry *dtmp; struct kernfs_node *kntmp; if (kn == knparent) return dentry; kntmp = find_next_ancestor(kn, knparent); if (WARN_ON(!kntmp)) { dput(dentry); return ERR_PTR(-EINVAL); } dtmp = lookup_positive_unlocked(kntmp->name, dentry, strlen(kntmp->name)); dput(dentry); if (IS_ERR(dtmp)) return dtmp; knparent = kntmp; dentry = dtmp; } while (true); } static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc) { struct kernfs_super_info *info = kernfs_info(sb); struct kernfs_root *kf_root = kfc->root; struct inode *inode; struct dentry *root; info->sb = sb; /* Userspace would break if executables or devices appear on sysfs */ sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; sb->s_blocksize = PAGE_SIZE; sb->s_blocksize_bits = PAGE_SHIFT; sb->s_magic = kfc->magic; sb->s_op = &kernfs_sops; sb->s_xattr = kernfs_xattr_handlers; if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP) sb->s_export_op = &kernfs_export_ops; sb->s_time_gran = 1; /* sysfs dentries and inodes don't require IO to create */ sb->s_shrink.seeks = 0; /* get root inode, initialize and unlock it */ down_read(&kf_root->kernfs_rwsem); inode = kernfs_get_inode(sb, info->root->kn); up_read(&kf_root->kernfs_rwsem); if (!inode) { pr_debug("kernfs: could not get root inode\n"); return -ENOMEM; } /* instantiate and link root dentry */ root = d_make_root(inode); if (!root) { pr_debug("%s: could not get root dentry!\n", __func__); return -ENOMEM; } sb->s_root = root; sb->s_d_op = &kernfs_dops; return 0; } static int kernfs_test_super(struct super_block *sb, struct fs_context *fc) { struct kernfs_super_info *sb_info = kernfs_info(sb); struct kernfs_super_info *info = fc->s_fs_info; return sb_info->root == info->root && sb_info->ns == info->ns; } static int kernfs_set_super(struct super_block *sb, struct fs_context *fc) { struct kernfs_fs_context *kfc = fc->fs_private; kfc->ns_tag = NULL; return set_anon_super_fc(sb, fc); } /** * kernfs_super_ns - determine the namespace tag of a kernfs super_block * @sb: super_block of interest * * Return the namespace tag associated with kernfs super_block @sb. */ const void *kernfs_super_ns(struct super_block *sb) { struct kernfs_super_info *info = kernfs_info(sb); return info->ns; } /** * kernfs_get_tree - kernfs filesystem access/retrieval helper * @fc: The filesystem context. * * This is to be called from each kernfs user's fs_context->ops->get_tree() * implementation, which should set the specified ->@fs_type and ->@flags, and * specify the hierarchy and namespace tag to mount via ->@root and ->@ns, * respectively. */ int kernfs_get_tree(struct fs_context *fc) { struct kernfs_fs_context *kfc = fc->fs_private; struct super_block *sb; struct kernfs_super_info *info; int error; info = kzalloc(sizeof(*info), GFP_KERNEL); if (!info) return -ENOMEM; info->root = kfc->root; info->ns = kfc->ns_tag; INIT_LIST_HEAD(&info->node); fc->s_fs_info = info; sb = sget_fc(fc, kernfs_test_super, kernfs_set_super); if (IS_ERR(sb)) return PTR_ERR(sb); if (!sb->s_root) { struct kernfs_super_info *info = kernfs_info(sb); struct kernfs_root *root = kfc->root; kfc->new_sb_created = true; error = kernfs_fill_super(sb, kfc); if (error) { deactivate_locked_super(sb); return error; } sb->s_flags |= SB_ACTIVE; down_write(&root->kernfs_rwsem); list_add(&info->node, &info->root->supers); up_write(&root->kernfs_rwsem); } fc->root = dget(sb->s_root); return 0; } void kernfs_free_fs_context(struct fs_context *fc) { /* Note that we don't deal with kfc->ns_tag here. */ kfree(fc->s_fs_info); fc->s_fs_info = NULL; } /** * kernfs_kill_sb - kill_sb for kernfs * @sb: super_block being killed * * This can be used directly for file_system_type->kill_sb(). If a kernfs * user needs extra cleanup, it can implement its own kill_sb() and call * this function at the end. */ void kernfs_kill_sb(struct super_block *sb) { struct kernfs_super_info *info = kernfs_info(sb); struct kernfs_root *root = info->root; down_write(&root->kernfs_rwsem); list_del(&info->node); up_write(&root->kernfs_rwsem); /* * Remove the superblock from fs_supers/s_instances * so we can't find it, before freeing kernfs_super_info. */ kill_anon_super(sb); kfree(info); } static void __init kernfs_mutex_init(void) { int count; for (count = 0; count < NR_KERNFS_LOCKS; count++) mutex_init(&kernfs_locks->open_file_mutex[count]); } static void __init kernfs_lock_init(void) { kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL); WARN_ON(!kernfs_locks); kernfs_mutex_init(); } void __init kernfs_init(void) { kernfs_node_cache = kmem_cache_create("kernfs_node_cache", sizeof(struct kernfs_node), 0, SLAB_PANIC, NULL); /* Creates slab cache for kernfs inode attributes */ kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache", sizeof(struct kernfs_iattrs), 0, SLAB_PANIC, NULL); kernfs_lock_init(); }